On Mon, 2016-09-26 at 14:00 +0300, Denis Kirjanov wrote: > > > On Wednesday, September 21, 2016, Denis Kirjanov <kda@linux-powerpc.o > rg> wrote: > > That's unclear why lockdep shows the following warning but adding a > > lockdep class to struct pmac_i2c_bus solves it > > HI Ben, > > could you give any comments on this?
I haven't quite figured out real reason for lockdep complaint, the output is as usual terribly hard to parse, but adding a lock class doesn't sound like something wrong to do so ... Ben. > Thanks! > > > > [ 20.507795] > > ====================================================== > > [ 20.507796] [ INFO: possible circular locking dependency > > detected ] > > [ 20.507800] 4.8.0-rc7-00037-gd2ffb01 #21 Not tainted > > [ 20.507801] ---------------------------------------------------- > > --- > > [ 20.507803] swapper/0/1 is trying to acquire lock: > > [ 20.507818] (&bus->mutex){+.+.+.}, at: [<c000000000052830>] > > .pmac_i2c_open+0x30/0x100 > > [ 20.507819] > > [ 20.507819] but task is already holding lock: > > [ 20.507829] (&policy->rwsem){+.+.+.}, at: [<c00000000068adcc>] > > .cpufreq_online+0x1ac/0x9d0 > > [ 20.507830] > > [ 20.507830] which lock already depends on the new lock. > > [ 20.507830] > > [ 20.507832] > > [ 20.507832] the existing dependency chain (in reverse order) is: > > [ 20.507837] > > [ 20.507837] -> #4 (&policy->rwsem){+.+.+.}: > > [ 20.507844] [<c00000000082385c>] .down_write+0x6c/0x110 > > [ 20.507849] [<c00000000068adcc>] > > .cpufreq_online+0x1ac/0x9d0 > > [ 20.507855] [<c0000000004d76d8>] > > .subsys_interface_register+0xb8/0x110 > > [ 20.507860] [<c000000000689bb0>] > > .cpufreq_register_driver+0x1d0/0x250 > > [ 20.507866] [<c000000000b4f8f4>] > > .g5_cpufreq_init+0x9cc/0xa28 > > [ 20.507872] [<c00000000000a98c>] > > .do_one_initcall+0x5c/0x1d0 > > [ 20.507878] [<c000000000b0f86c>] > > .kernel_init_freeable+0x1ac/0x28c > > [ 20.507883] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 > > [ 20.507887] [<c0000000000098f4>] > > .ret_from_kernel_thread+0x58/0x64 > > [ 20.507894] > > [ 20.507894] -> #3 (subsys mutex#2){+.+.+.}: > > [ 20.507899] [<c000000000820448>] > > .mutex_lock_nested+0xa8/0x590 > > [ 20.507903] [<c0000000004d7f24>] > > .bus_probe_device+0x44/0xe0 > > [ 20.507907] [<c0000000004d5208>] .device_add+0x508/0x730 > > [ 20.507911] [<c0000000004dd528>] > > .register_cpu+0x118/0x190 > > [ 20.507916] [<c000000000b14450>] > > .topology_init+0x148/0x248 > > [ 20.507921] [<c00000000000a98c>] > > .do_one_initcall+0x5c/0x1d0 > > [ 20.507925] [<c000000000b0f86c>] > > .kernel_init_freeable+0x1ac/0x28c > > [ 20.507929] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 > > [ 20.507934] [<c0000000000098f4>] > > .ret_from_kernel_thread+0x58/0x64 > > [ 20.507939] > > [ 20.507939] -> #2 (cpu_add_remove_lock){+.+.+.}: > > [ 20.507944] [<c000000000820448>] > > .mutex_lock_nested+0xa8/0x590 > > [ 20.507950] [<c000000000087a9c>] > > .register_cpu_notifier+0x2c/0x70 > > [ 20.507955] [<c000000000b267e0>] > > .spawn_ksoftirqd+0x18/0x4c > > [ 20.507959] [<c00000000000a98c>] > > .do_one_initcall+0x5c/0x1d0 > > [ 20.507964] [<c000000000b0f770>] > > .kernel_init_freeable+0xb0/0x28c > > [ 20.507968] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 > > [ 20.507972] [<c0000000000098f4>] > > .ret_from_kernel_thread+0x58/0x64 > > [ 20.507978] > > [ 20.507978] -> #1 (&host->mutex){+.+.+.}: > > [ 20.507982] [<c000000000820448>] > > .mutex_lock_nested+0xa8/0x590 > > [ 20.507987] [<c0000000000527e8>] .kw_i2c_open+0x18/0x30 > > [ 20.507991] [<c000000000052894>] > > .pmac_i2c_open+0x94/0x100 > > [ 20.507995] [<c000000000b220a0>] > > .smp_core99_probe+0x260/0x410 > > [ 20.507999] [<c000000000b185bc>] > > .smp_prepare_cpus+0x280/0x2ac > > [ 20.508003] [<c000000000b0f748>] > > .kernel_init_freeable+0x88/0x28c > > [ 20.508008] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 > > [ 20.508012] [<c0000000000098f4>] > > .ret_from_kernel_thread+0x58/0x64 > > [ 20.508018] > > [ 20.508018] -> #0 (&bus->mutex){+.+.+.}: > > [ 20.508023] [<c0000000000ed5b4>] .lock_acquire+0x84/0x100 > > [ 20.508027] [<c000000000820448>] > > .mutex_lock_nested+0xa8/0x590 > > [ 20.508032] [<c000000000052830>] > > .pmac_i2c_open+0x30/0x100 > > [ 20.508037] [<c000000000052e14>] > > .pmac_i2c_do_begin+0x34/0x120 > > [ 20.508040] [<c000000000056bc0>] .pmf_call_one+0x50/0xd0 > > [ 20.508045] [<c00000000068ff1c>] > > .g5_pfunc_switch_volt+0x2c/0xc0 > > [ 20.508050] [<c00000000068fecc>] > > .g5_pfunc_switch_freq+0x1cc/0x1f0 > > [ 20.508054] [<c00000000068fc2c>] > > .g5_cpufreq_target+0x2c/0x40 > > [ 20.508058] [<c0000000006873ec>] > > .__cpufreq_driver_target+0x23c/0x840 > > [ 20.508062] [<c00000000068c798>] > > .cpufreq_gov_performance_limits+0x18/0x30 > > [ 20.508067] [<c00000000068915c>] > > .cpufreq_start_governor+0xac/0x100 > > [ 20.508071] [<c00000000068a788>] > > .cpufreq_set_policy+0x208/0x260 > > [ 20.508076] [<c00000000068abdc>] > > .cpufreq_init_policy+0x6c/0xb0 > > [ 20.508081] [<c00000000068ae70>] > > .cpufreq_online+0x250/0x9d0 > > [ 20.508085] [<c0000000004d76d8>] > > .subsys_interface_register+0xb8/0x110 > > [ 20.508090] [<c000000000689bb0>] > > .cpufreq_register_driver+0x1d0/0x250 > > [ 20.508094] [<c000000000b4f8f4>] > > .g5_cpufreq_init+0x9cc/0xa28 > > [ 20.508099] [<c00000000000a98c>] > > .do_one_initcall+0x5c/0x1d0 > > [ 20.508103] [<c000000000b0f86c>] > > .kernel_init_freeable+0x1ac/0x28c > > [ 20.508107] [<c00000000000b3bc>] .kernel_init+0x1c/0x140 > > [ 20.508112] [<c0000000000098f4>] > > .ret_from_kernel_thread+0x58/0x64 > > [ 20.508113] > > [ 20.508113] other info that might help us debug this: > > [ 20.508113] > > [ 20.508121] Chain exists of: > > [ 20.508121] &bus->mutex --> subsys mutex#2 --> &policy->rwsem > > [ 20.508121] > > [ 20.508123] Possible unsafe locking scenario: > > [ 20.508123] > > [ 20.508124] CPU0 CPU1 > > [ 20.508125] ---- ---- > > [ 20.508128] lock(&policy->rwsem); > > [ 20.508132] lock(subsys mutex#2); > > [ 20.508135] lock(&policy->rwsem); > > [ 20.508138] lock(&bus->mutex); > > [ 20.508139] > > [ 20.508139] *** DEADLOCK *** > > [ 20.508139] > > [ 20.508141] 3 locks held by swapper/0/1: > > [ 20.508150] #0: (cpu_hotplug.lock){++++++}, at: > > [<c000000000087838>] .get_online_cpus+0x48/0xc0 > > [ 20.508159] #1: (subsys mutex#2){+.+.+.}, at: > > [<c0000000004d7670>] .subsys_interface_register+0x50/0x110 > > [ 20.508168] #2: (&policy->rwsem){+.+.+.}, at: > > [<c00000000068adcc>] .cpufreq_online+0x1ac/0x9d0 > > [ 20.508169] > > [ 20.508169] stack backtrace: > > [ 20.508173] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc7- > > 00037-gd2ffb01 #21 > > [ 20.508175] Call Trace: > > [ 20.508180] [c0000000790c2b90] [c00000000082cc70] > > .dump_stack+0xe0/0x14c (unreliable) > > [ 20.508184] [c0000000790c2c20] [c000000000828c88] > > .print_circular_bug+0x350/0x388 > > [ 20.508188] [c0000000790c2cd0] [c0000000000ecb0c] > > .__lock_acquire+0x196c/0x1d30 > > [ 20.508192] [c0000000790c2e50] [c0000000000ed5b4] > > .lock_acquire+0x84/0x100 > > [ 20.508196] [c0000000790c2f20] [c000000000820448] > > .mutex_lock_nested+0xa8/0x590 > > [ 20.508201] [c0000000790c3030] [c000000000052830] > > .pmac_i2c_open+0x30/0x100 > > [ 20.508206] [c0000000790c30c0] [c000000000052e14] > > .pmac_i2c_do_begin+0x34/0x120 > > [ 20.508209] [c0000000790c3150] [c000000000056bc0] > > .pmf_call_one+0x50/0xd0 > > [ 20.508213] [c0000000790c31e0] [c00000000068ff1c] > > .g5_pfunc_switch_volt+0x2c/0xc0 > > [ 20.508217] [c0000000790c3250] [c00000000068fecc] > > .g5_pfunc_switch_freq+0x1cc/0x1f0 > > [ 20.508221] [c0000000790c3320] [c00000000068fc2c] > > .g5_cpufreq_target+0x2c/0x40 > > [ 20.508226] [c0000000790c3390] [c0000000006873ec] > > .__cpufreq_driver_target+0x23c/0x840 > > [ 20.508230] [c0000000790c3440] [c00000000068c798] > > .cpufreq_gov_performance_limits+0x18/0x30 > > [ 20.508235] [c0000000790c34b0] [c00000000068915c] > > .cpufreq_start_governor+0xac/0x100 > > [ 20.508239] [c0000000790c3530] [c00000000068a788] > > .cpufreq_set_policy+0x208/0x260 > > [ 20.508244] [c0000000790c35d0] [c00000000068abdc] > > .cpufreq_init_policy+0x6c/0xb0 > > [ 20.508249] [c0000000790c3940] [c00000000068ae70] > > .cpufreq_online+0x250/0x9d0 > > [ 20.508253] [c0000000790c3a30] [c0000000004d76d8] > > .subsys_interface_register+0xb8/0x110 > > [ 20.508258] [c0000000790c3ad0] [c000000000689bb0] > > .cpufreq_register_driver+0x1d0/0x250 > > [ 20.508262] [c0000000790c3b60] [c000000000b4f8f4] > > .g5_cpufreq_init+0x9cc/0xa28 > > [ 20.508267] [c0000000790c3c20] [c00000000000a98c] > > .do_one_initcall+0x5c/0x1d0 > > [ 20.508271] [c0000000790c3d00] [c000000000b0f86c] > > .kernel_init_freeable+0x1ac/0x28c > > [ 20.508276] [c0000000790c3db0] [c00000000000b3bc] > > .kernel_init+0x1c/0x140 > > [ 20.508280] [c0000000790c3e30] [c0000000000098f4] > > .ret_from_kernel_thread+0x58/0x64 > > > > Signed-off-by: Denis Kirjanov <k...@linux-powerpc.org> > > --- > > arch/powerpc/platforms/powermac/low_i2c.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/arch/powerpc/platforms/powermac/low_i2c.c > > b/arch/powerpc/platforms/powermac/low_i2c.c > > index 6d6f277..0159363 100644 > > --- a/arch/powerpc/platforms/powermac/low_i2c.c > > +++ b/arch/powerpc/platforms/powermac/low_i2c.c > > @@ -90,6 +90,7 @@ struct pmac_i2c_bus > > int opened; > > int polled; /* open mode */ > > struct platform_device *platform_dev; > > + struct lock_class_key lock_key; > > > > /* ops */ > > int (*open)(struct pmac_i2c_bus *bus); > > @@ -587,6 +588,7 @@ static void __init kw_i2c_add(struct > > pmac_i2c_host_kw *host, > > bus->close = kw_i2c_close; > > bus->xfer = kw_i2c_xfer; > > mutex_init(&bus->mutex); > > + lockdep_set_class(&bus->mutex, &bus->lock_key); > > if (controller == busnode) > > bus->flags = pmac_i2c_multibus; > > list_add(&bus->link, &pmac_i2c_busses); > > @@ -815,6 +817,7 @@ static void __init pmu_i2c_probe(void) > > bus->hostdata = bus + 1; > > bus->xfer = pmu_i2c_xfer; > > mutex_init(&bus->mutex); > > + lockdep_set_class(&bus->mutex, &bus->lock_key); > > bus->flags = pmac_i2c_multibus; > > list_add(&bus->link, &pmac_i2c_busses); > > > > @@ -938,6 +941,7 @@ static void __init smu_i2c_probe(void) > > bus->hostdata = bus + 1; > > bus->xfer = smu_i2c_xfer; > > mutex_init(&bus->mutex); > > + lockdep_set_class(&bus->mutex, &bus->lock_key); > > bus->flags = 0; > > list_add(&bus->link, &pmac_i2c_busses); > > > > -- > > 2.4.0 > > > >